1. Field of the Invention
This invention relates generally to apparatus and methods for manufacturing optical and photonic devices by employing the micro-opto-electro-mechanical system (MOEMS) technologies. More particularly, this invention is related to configuration and method of manufacturing tunable Fabry-Perot cavity by applying a bulk micro-machining process on a supporting substrate to improve the production yield with reduced process irregularities produced by conventional surface micro-machining processes.
2. Description of the Related Art
Recent development of the optical device manufacture technologies is still faced with a technical difficulty that the support substrate for the freestanding membrane is often produced with undercut irregularities caused by conventional surface micro-machining process in forming the membrane. These undercut irregularities often cause a reduction of production yield and limit the usefulness of the micro-opto-electro-mechanical system (MOEMS) technologies in manufacturing micro-optical devices with mass production at further reduced production costs. Current manufacturing processes apply a surface micro-machining technique uses oxide or phosphorous doped silicate glass (PSG) as the sacrificial etch materials. Meanwhile, the sacrificial etch layer composed of the PSG material is also implemented as structural elements in the optical device formed as the chamber poles. A typical example is the optical modulators implemented with the configuration of a mechanical anti-reflection (MAR) switch. The manufacture irregularities produced by applying the dry or wet etching processes and using the conventional sacrificial etch materials adversely affect the production yields and the switching/attenuation performance and also the reliability of the devices. The next generation broadband optical communication system requires significant scale-down of size and reduction in production costs from current standards based on technology of devices by mechanically assembling optical components. Recent development of silicon based optical single switch modulator and integrated multiple-channel attenuation/switching modules provides first step in a pathway of achieving improvement to provide optical devices suitable for next generation system applications. However, the irregularities of the supporting structure for a freestanding membrane caused by the ineffectiveness of the stop etching configuration due to sacrificial layer undercut in the membrane forming processes often limit the applications and production yields when such technologies are applied.
Therefore, a still need exists in the art in the field of the optical signal transmission systems to provide a configuration and method of manufacture to overcome such difficulties and limitations. It is desirable that such method can provide simplified manufacturing processes such that cost reduction and production yield together with the product reliability can be improved. In addition, it is further desired that more process control can be provided for more precisely controlling the manufacturing processes to produce optical devices with size and dimensions with better controlled accuracy.
It is therefore an object of the present invention to provide new and improved configuration and methods for manufacturing optical devices to substantially eliminate the undercut irregularities on a supporting substrate such that the problems and difficulties as encountered in the prior art may be resolved.
Specifically, it is the object of this invention to provide new and improved manufacture methods and configurations to form well-defined cavity by applying a bulk micro-machining process on the supporting substrate to eliminate the cavity undercut irregularities resulted from conventional etching processes. Instead of applying a surface micro-machining process to form the freestanding membrane by etching through an etching window opened on the top surface, a bulk machining process is employed to remove an entire portion below a membrane. The poles of the chamber are formed as spacer layer surrounding the freestanding membrane. The Fabry-Perot cavity is formed by stacking and face-to-face bonding the spacers with the freestanding membrane disposed at a distance away from each other to form a resonant cavity between the membranes.
Briefly, in a preferred embodiment, this invention discloses a method for forming an optical device on a substrate. The method includes the steps of a) forming a membrane layer on a top surface of the substrate. And, b) applying a bulk micro-machining process for etching off an entire bulk portion of the substrate below the membrane layer whereby the membrane layer becoming a freestanding membrane layer above the entire bulk portion that is etched off. In a preferred embodiment, the step a) of forming a membrane layer further includes a step of forming the membrane layer with a bulk-etch protection bottom layer on the top surface of said substrate. With an etch-protection bottom layer, the membrane layer will remain intact when the bulk micro-machining process is applied to remove the entire bulk portion underneath the membrane layer.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the various drawing figures.